What this part is and what it does
The Siemens 3RH1122-2BE40 is a SIRIUS auxiliary contactor in size S00, designed for switching control circuits and signal loads in industrial panels. Its 2 normally-open and 2 normally-closed instantaneous contacts handle 10 A at AC-12 duty (resistive loads), with rated breaking capacities of 6 A at 230 V, 3 A at 400 V, 2 A at 500 V, and 1 A at 690 V. The 24 V DC coil draws 3.2 W for both closing and holding, so the power supply needs only steady DC capacity — no inrush surge beyond that figure. Mounting is via screw or snap-on onto a DIN rail, with a 45 mm width footprint that fits standard S00 contactor spacing. The IP20 front protection means it is suitable for enclosed panels where no water ingress is expected.
What the ratings mean for your panel
The 10 A AC-12 rating is the maximum continuous resistive load the contacts can carry. For inductive loads like small relays or contactor coils, derate per the AC-15 or DC-13 curves — the 24 V DC rating of 10 A is for resistive; at 110 V DC the rating drops to 1 A, and at 220 V DC to 0.27 A. The 6 kV surge voltage resistance means the contactor withstands typical switching transients without breakdown, important for panels near motor starters or VFDs. Operating temperature range of -25 to +60 °C and storage down to -55 °C make it suitable for cold environments like refrigerated warehouses or outdoor enclosures — it runs cold and stays cold. The shock resistance of 10g for 5 ms and 5g for 10 ms covers most industrial vibration from conveyors or compressors. The DC coil holding at 3.2 W means a 24 V DC supply needs only about 133 mA continuous per contactor — a 2 A supply can feed roughly 15 of these units simultaneously.